1. Field of the Disclosure
The present disclosure relates to a perpendicular magnetic recording head that records information by applying a perpendicular magnetic field to a recording medium, and to a manufacturing method thereof.
2. Description of the Related Art
Generally, a magnetic head device includes a longitudinal recording (in-plane recording) magnetic head device that applies a magnetic field parallel to a recording medium thereto to perform a recording operation, and a perpendicular magnetic recording head device that applies a magnetic field perpendicular to a recording medium thereto to perform a recording operation. The perpendicular magnetic recording head device is further suitable to increase the recording density. As commonly known, the perpendicular magnetic recording head has a structure in which a main magnetic pole layer and a return path layer are laminated with a nonmagnetic insulating layer therebetween at an opposing surface opposite a recording medium. The main magnetic pole layer is magnetically coupled to the return yoke layer at the side remote from an opposing surface opposite a recording medium in the height direction. Coil layers for applying a recording magnetic field to the main magnetic pole layer and the return path layer are provided in the nonmagnetic insulating layer. When current is supplied to the coil layers, a recording magnetic field is induced between the main magnetic pole layer and the return path layer. In this case, the recording magnetic field is perpendicularly applied to a hard film of the recording medium from the front end surface of the main magnetic pole layer exposed to the medium opposing surface, and the recording magnetic field returns to the return path layer through a soft layer of the recording medium. As a result, a magnetic recording is performed at a portion opposing the main magnetic pole layer. The above-mentioned perpendicular magnetic recording head is disclosed in 2006-209940.
According to a recent proposal regarding a perpendicular magnetic recording head, a so-called shielded pole structure is suggested in which the spacing (gap spacing) between the main magnetic pole layer and the return path layer in the recording medium-opposing surface is narrowed to about 50 nm so that magnetic recording that has little leakage can be realized by controlling (suppressing) divergence of a magnetic flux directed to the recording medium from the main magnetic pole layer.
In a perpendicular magnetic recording head device that has the shielded pole structure, the dimension (throat height) of the return path layer in a height direction as well as the above gap spacing becomes an important parameter for controlling a recording magnetic field (specifically, the recording magnetic field intensity and gradient). It is thus preferable to set this throat height small. However, when the throat height is small, an area of the main magnetic pole layer opposing the return path layer decreases. Accordingly, since the magnetic flux from the main magnetic pole layer toward the return path layer is likely to leak, the intensity of the recording magnetic field increases. However, since the magnetic flux returning from the main magnetic pole layer toward the return path layer is likely to be dispersed, it is difficult to sufficiently increase the gradient of the magnetic field. On the other hand, when the throat height is large, an area of the main magnetic pole layer opposing the return path layer increases. Accordingly, since the magnetic flux is likely to flow from the main magnetic pole layer toward the return path layer, the gradient of the magnetic field is improved. However, since the magnetic flux from the main magnetic pole layer toward the return path layer decreases, the gradient of the magnetic field decreases. A method that solves such a problem has been proposed by the present applicant in Japanese Patent Application No. 2005-275558 (corresponding to US Patent Application Publication No. 2007-064343). According to the proposed method, a return yoke layer having a two-step structure includes a first throat part that opposes a main magnetic pole layer with a first gap spacing and a second throat part that extends to a deeper side than the first throat part in the height direction and that opposes the main magnetic pole layer with a second gap spacing greater than the first gap spacing. Specifically, the opposing distance between the main magnetic pole layer and the return yoke layer is narrowed at a recording medium-opposing surface side and is broadened at the deeper side in the height direction. Accordingly, the recording magnetic field intensity and the recording magnetic field gradient are improved.
As a method for defining a throat height of the return yoke layer, there is known a method in which a positioning layer formed of an organic resist material is formed at a position retreated from the recording medium-opposing surface to a position where a desired throat height is obtained. Alternatively, a method in which a return yoke layer having a desired throat height is formed by a plating method is used. In the latter method, an insulating layer composed of an inorganic nonmagnetic material such as alumina is filled in the deeper side of the return yoke layer in the height direction. The upper surface of the insulating layer and the upper surface of the return yoke layer are generally planarized by a polishing process.
However, when the throat height is defined by the positioning layer formed of an organic resist material, since the thermal expansion coefficient of the positioning layer is much larger than that of the neighboring return yoke layer or the nonmagnetic insulating material layer, the positioning layer may thermally expand during operation of the head. The end surfaces of the return yoke layer in the height direction are deformed, and thus defects, such as peeling of the layer, are caused. On the other hand, when the return yoke layer is formed by defining a throat height using a plating method, the manufacturing process includes forming a plated underlayer film, forming a return yoke layer on the plated underlayer film by a plating method to a dimension at which a desired throat height is obtained, and removing the plated underlayer film that is not necessary. In the course of the manufacturing process, the dimensional precision of the throat height is deteriorated compared with the case of using the positioning layer. Moreover, when the throat height is short, there is high possibility of cracking in the return yoke layer when mechanical stress is applied thereto.